Unmanned remote control rotary aircraft have recently become popular for recreation and also in larger and more sophisticated versions for surveillance by military and police personnel. One popular configuration includes a number of arms extending laterally from the aircraft body, with a rotor assembly on the end of each arm. The rotor assemblies sometimes have upper and lower rotors that rotate in opposite directions to avoid exerting torque on the body which would cause it to spin.
Where the rotor assemblies have a single rotor, torque on the body from the rotational motion of the rotors is avoided by having the rotors rotate in opposite directions. The vertical lift is the same, but the torque imparted by rotation in one direction is cancelled out by the rotation in the opposite direction. Where an even number of arms and rotor assemblies is used, the rotational forces cancel each other and the body is substantially stable.
Where an uneven number of arms and rotor assemblies is used, such as in the popular three rotor configuration, two rotors spin in one direction and the third spins in the opposite direction. The rotational axis of the third rotor is then tilted slightly away from vertical so it exerts a horizontal force component that counteracts the torque force exerted by the other rotors, again resulting in a stable body. The degree of tilt can be adjusted by rotating the arm to adjust for varying rotor speeds.
Such multi-rotor unmanned remote control rotary aircraft are disclosed for example in U.S. Pat. Nos. 8,052,081 and 8,292,215 to the present inventors Olm et al. To make the aircraft more compact for storage and transport the rotors can be removed and the arms folded into a side by side orientation. Although not shown in the patents, a leg assembly is typically attached to the bottom of the aircraft body, and to support the aircraft on the ground in the necessary orientation for landing and takeoff.